Brucella abortus RNA mimics the inhibition of major histocompatibility complex class I expression mediated by Brucella abortus on human monocytes

MILILLO AYELÉN; VELAZQUEZ LIS NOELIA; DELPINO M. VICTORIA; POZNER ROBERTO; GIAMBARTOLOMEI GUILLERMO H; BARRIONUEVO PAULA

Congreso; 30. Phagocytes - Gordon Research Conference. Waterville Valley, NH, USA. 31 de Mayo al 5 de Junio de 2015.; 2015

Brucella abortus is an intracellular Gram-negativebacterium that infects wild and domestic animals and can be transmitted tohumans. Upon infection, Brucella elicitsa vigorous Th1 immune response which activates cytotoxic T lymphocytes. However, B. abortus is able to persist inside its host and establishesa chronic infection. Werecently reported that infection of human monocytes/macrophages with B. abortus inhibits the IFN-γ-inducedMHC-I cell surface expression down-modulatingcytotoxic CD8+ T cell responses. MHC-I down-modulationdepends on bacterial viability and results from the capacity of B. abortus to retain the MHC-I moleculeswithin the Golgi apparatus. However, the components of B. abortus involved in this phenomenon remained unknown.Prokaryotic RNA has been recently characterizedas a special class of viability-associated PAMPs (vita-PAMPs). Thus, the aim of this study was to evaluate theeffect of B. abortus RNA on IFN-g-induced MHC-I expression on human monocytes. Forthis, THP-1 cells were incubated with B. abortus RNA (0.1-20 µg/ml) in thepresence of IFN-g for 48 h. The expressionof MHC-I molecules (HLA-ABC) was then evaluated by flow cytometry. B. abortus RNA significantly (p<0.05) down-regulatedthe IFN-g-induced surfaceexpression of MHC-I molecules in a dose-dependent fashion. Accordingly, when THP-1 cells werestimulated with heat-killed B. abortus ordifferent structural components of the bacteria (lipoproteins, LPS or DNA),MHC-I down-modulation was not observed. By confocal microscopy, we alsodemonstrated that B. abortus RNAmimics the intracellular retention within the Golgi apparatus of MHC-Imolecules observed with the infection. Interestingly, significant MHC-Idown-regulation (p<0.05) was obtainedwith Salmonella typhimurium and Bacillus cereus (Gram-negative and Gram-positivebacteria respectively) RNAs but not with PBMCs RNA, indicating that the effectcould be extended to other prokaryotic but not eukaryotic RNAs. Overall, theseresults indicate that the vita-PAMPRNA is a component employed by B. abortusto inhibit MHC-I expression whereby the bacteria could evade the cytotoxicCD8+ T cell immunological surveillance establishing a chronic infection.